I used PlanarReflections for my VR Project as well. I used them for glass walls and I’m pretty satisfied with the quality. I will attach some screenshots (scene and settings).
Maybe try using my settings and see if this works for you.
I got a pretty stable framerate, even with multiple planar reflections in one scene (most of the time around 90 fps, and this is with GTX 980 at my “old” office workplace).
Hope this helps 